Does anyone have any good like about how NTL broadband works after data has left your PC. Ie, from the point it hits the STB, how it is routed onto the internet. How is it different from BT ADSL. Also, what equipment is used, what type of lines etc.

Rather than re-invent the wheel, this link will show you how a cable modem works, pretty much the same as your STB.
If you would like to know more about NTL's specific equipment after you have read through the link, don't hesitate to contact me